feat(simulator): add GUI runner, stubs, and workspace assets

Add host simulator scaffolding, examples, and docs so led-driver main can run end-to-end with MicroPython module stubs.

Co-authored-by: Cursor <cursoragent@cursor.com>

stubs/neopixel.py

@@ -0,0 +1,37 @@
+"""Host NeoPixel: keeps RGB buffer and notifies the GUI on `write()`."""
+
+# Set by led-simulator main: callable(list[tuple[int,int,int]]) -> None
+PIXEL_SINK = None
+
+
+class NeoPixel:
+    def __init__(self, pin, n):
+        self.pin = pin
+        self.n = n
+        self._buf = [(0, 0, 0)] * n
+
+    def __setitem__(self, index, value):
+        if isinstance(value, (list, tuple)) and len(value) >= 3:
+            r, g, b = (int(value[0]), int(value[1]), int(value[2]))
+            self._buf[index] = (
+                max(0, min(255, r)),
+                max(0, min(255, g)),
+                max(0, min(255, b)),
+            )
+
+    def __getitem__(self, index):
+        return self._buf[index]
+
+    def fill(self, color):
+        c = (0, 0, 0)
+        if isinstance(color, (list, tuple)) and len(color) >= 3:
+            c = (
+                max(0, min(255, int(color[0]))),
+                max(0, min(255, int(color[1]))),
+                max(0, min(255, int(color[2]))),
+            )
+        self._buf = [c] * self.n
+
+    def write(self):
+        if PIXEL_SINK is not None:
+            PIXEL_SINK(list(self._buf))